1. Field of the Invention
This invention relates to a hose used for conveying a refrigerant containing an ester oil, or a similar electrically insulating oil, as a refrigerator oil (lubricant) to an electrically driven compressor. This invention is suitable for use with, among others, an electrically driven compressor in an automobile air conditioner.
2. Description of the Related Art
FIG. 1 shows by way of example a hose which has hitherto been used for transporting a refrigerant to an engine driven compressor in an automobile air conditioner. It comprises an inner tube 1 of rubber, such as IIR (butyl rubber), a reinforcing layer 2 formed by e.g. braided fiber and an outer tube 3 of rubber, such as EPDM (ethylene-propylene-diene rubber). This structure has been employed to give the hose resistance to vibration, and resistance and impermeability to a refrigerant composed of a refrigerator oil of the PAG (polyalkylene glycol) type and a flon (e.g. Freon) substitute, such as HFC (hydrofluorocarbon).
A hybrid car driven by both a gasoline engine and an electric motor, and an economical car having a gasoline engine adapted to stop instead of idling are being developed for practical use to avoid the global environmental problems caused by the massive consumption of gasoline. In either event, the air conditioner which can be employed is of the type in which an electrically driven compressor is employed instead of an engine driven one which does not work if the engine is stopped.
An electrically driven compressor is required to have a high degree of electric insulation, since a motor is installed in a refrigerator. Accordingly, it is necessary to change the refrigerator oil of the PAG type to an ester oil, such as POE (polyol ester), having a high degree of electrically insulating property. It is necessary to ensure a high degree of waterproofness against an external source in order to maintain the high electric insulation of the compressor and avoid the hydrolysis of the ester oil.
It has, however, been a drawback of the hose as shown in FIG. 1 that the IIR forming the inner tube 1 is likely to swell easily with an insulating oil, such as an ester oil, and cannot be expected to be satisfactorily resistant or impermeable to any refrigerant for an electrically driven compressor. It has been another drawback thereof that the hose as a whole is not so designed as to be highly waterproof, but fails to resist any invasion of water through its wall from an external source satisfactorily.
Although no such problem may arise from a metal pipe used for transporting a refrigerant to an electrically driven compressor in a cabinet refrigerator, etc., it is impossible to use a metal pipe for transporting a refrigerant to a compressor in an automobile air conditioner, since a metal pipe is too rigid to withstand vibration of the moving automobile, or its engine.